Pulmonary capillary blood flow pulsatility is being studied during systemic hypoxemia, alveolar hypoxia, or both together. This is an attempt to separate locally-medicated from systemically-medicated effects on the redistribution of pulmonary blood flow away from locally hypoxic areas of the lung. Nitrous oxide uptake in anesthetized days, measured by the pressure plethysmograph technique using a pneumatic differentiator, is used to measure pulmonary capillary blood flow. We are separating alveolar hypoxia from systemic hypoxemia and examining the influence of each on the pulsatility of pulmonary capillary flow.